The potato tuber moth, Phthorimaea operculella, is a major pest of potato, particularly under storage conditions. Due to the adverse effects of chemical pesticides on human health and the environment, as well as the development of insecticide resistance, there is a growing need for safer control alternatives. This study evaluated the efficacy of several isolates of Beauveria bassiana and Metarhizium anisopliae-collected from East Azarbaijan and Tehran provinces-along with a diatomaceous earth formulation (InsectoSec®) against the larvae of P. operculella. Bioassay results showed that the CS1 isolate of B. bassiana was the most effective, with an LC₅₀ of 6519 conidia/mL, while the DE isolate was the least effective, with an LC₅₀ of 89026 conidia/mL. The LC₅₀ for diatomaceous earth was 164 ppm. The time to symptom onset and mortality also varied among the isolates. The CS1 isolate demonstrated the lowest LT₅₀ values, at 1.68 days for the highest concentration and 20.16 days for the lowest concentration tested. The LT₅₀ for diatomaceous earth was 4.76 days at 500 ppm. Based on these findings, the SC1 isolate of M. anisopliae and the SA2 isolate of B. bassiana were identified as highly virulent. The diatomaceous earth formulation also exhibited acceptable control efficacy. In conclusion, both the identified fungal isolates and diatomaceous earth show promise as effective components in an integrated management program for the potato tuber moth.